The invention relates to rotors for electrical motors with a spherical magnetic air gap. Such motors now known as spherical motors have found an application to a large extent in pump construction. It has been shown that the design of spherical rotors featuring permanent magnets with low coercive force as described in U.S. Pat. No. 4,352,646, presents a great advantage over conventional rotors equipped with a squirrel cage. These magnets have semi-spherical configuration. This process utilizes materials which feature a comparably good electrical conductivity so that eddy currents are formed in the rotors, the motor being adapted to operate as an asynchronous motor during the start-up phase. As a result, oxide magnets are not suitable because their electrical conductivity is zero. Coercive force intensity should be so small that, when synchronous rpm has been reached, constant magnetization may occur through the magnetic flux of the stator. This can only be achieved by metal magnets.
The disadvantage of this solution is the fact that these magnets have been produced to date only by means of casting or sintering followed by high-temperature treatment and accordingly feature very wide manufacture tolerances. As a result, machinery is required which is costly in particular since the periphery of the magnet features a spherical surface and since the materials under consideration present exceptionally hard imbedments.
In addition, it has been shown that such parts cannot be produced with small wall thickness when made from a material which can be processed only in a powder metallurgical manner or which must be casted. For small motors within a power range of a few watts, caps with very small wall thickness are sufficient. Since these are technologically not feasible at this time, magnets must be utilized with unnecessarily thick walls. In addition, tolerances in the distribution of density of the materials in both production processes is so large that a significant effort must be made in the area of balancing. Also rotor impeller units supported in a way that permit tumbling movements require a counter weight on the impeller entrance heavy enough to compensate for the weight of the magnetic rotor. Unnecessarily heavy magnets therefore require unnecessarily heavy balancing masses. This may cause instability of the rotating rotor impeller unit which can tumble around the spherical bearing.